Abstract
The formation of Ar 2 + ions has been investigated by means of the threshold photoelectron photoion coincidence (TPEPICO) technique. Two pathways for the formation of Ar 2 + ions are important. One is a direct path via excitation of Rydberg states of Ar2 with consecutive autoionization. The other path is dissociative ionization of larger argon clusters, in this case argon trimers. These two pathways lead to Ar 2 + ions with different internal energy. The pathways are easily distinguished in the TPEPICO-TOF spectra by the kinetic energy released (KER) in the dissociative ionization. The KER for the reaction Ar 3 + → Ar 2 + + Ar was measured as a function of the photon energy and compared to the KER expected from statistical theory. The agreement is satisfying and confirms that Ar 3 + ions do indeed dissociate at the thermochemical threshold. At higher photon energy the excited2Π(3/2)g state of Ar 3 + is also detected from a second component in the KER. By applying a kinetic energy discrimination it is possible to measure cluster ion spectra in the presence of larger clusters but essentially without interference from the latter.
Published Version
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